The dirty secret to manufacturing is well-known to everyone in the sector: Great products are nothing without a great process to produce those products—and key to the mass production of almost every commercial and consumer are fixtures and jigs.

Many production processes use jigs and fixtures in quantity, and they are frequently unique to the specific operation they support—such as part holding for cutting, fastening, finishing or assembling—and it’s common to use dozens in the production of even a simple assembly. In highly competitive industries such as automotive manufacturing, the time and money spent on fixturing can be a pacing element in a new product program.

Additive manufacturing (AM) has all the characteristics needed to solve both cost and time problems simultaneously. Until recently, most AM equipment has been limited in the size of fixture that could be built, but the new generation of large format printers are changing these expectations. Leading this change are design and manufacturing engineers, with roles that frequently overlap with this new paradigm.

“A manufacturing engineer is not a CAD designer and ideally you want to take the CAD file and do the inverse of it,” said Frank Marangell, president of BigRep America. “Make a tool or fixture to hold that part, and then design another part or implement to interface with it. Two things can happen: You can have your designers do it, or you can train your manufacturing engineers to do it. But what we're trying to provide is a jigs-and-fixtures solution on your manufacturing floor. It’s where you go from software that takes the CAD data to send it to post-processing and through to implementation. That's the biggest challenge there.”

That challenge is complicated by the nature of the design process. Parts are designed for specific performance and cost objectives, and “easy to fixture” isn’t often part of the manufacturability discussion. As a result, manufacturing and tooling engineers frequently scramble to find a way to fixture large parts, complex parts or delicate parts—and sometimes parts with all three of those difficult attributes.

Historically, additive manufacturing has had limited use in large part fixturing due to the build envelope constraints of most machines. BigRep manufactures large build additive equipment, and the company expects large part fixturing for manufacturing will be a major market in 2020 and beyond. For many manufacturers, fixturing is a new application, even where prototype parts are commonly printed in-house. Prototyping and fixture-making are not mutually exclusive, says Marangell.

“Typically, a manufacturing engineer, manufacturing manager—or in a smaller shop, sometimes it's the owner—they’re all doing a manufacturing function. Previously, they may have had to wait for prototypes to exist first. By having additive, when you finish your design and make your first dozen prototypes, you can also send that data out to the manufacturing floor and create the tooling for the production lines. It’s possible that when your prototypes come in, you can actually have an assembly line make the parts in the real production environment and not just in some lab.”

The ability to make both short run parts and larger fixtures on the same additive machine not only saves time, but it pulls the design and build process in-house, avoiding the complexity of dealing with outside tooling shops. This siloed approach is not only slow, it’s risky.

“If you know, you're not going to do it,” says Marangell, adding, “The design guys throw the design over the wall, and then the manufacturing people have to live with it.”

Large format additive machines let design and manufacturing work together under the same roof, but parts are commonly much smaller than the tooling that supports manufacturing. Why use a large format machine such as the BigRep PRO one cubic meter machine, when the need for tooling is infrequent?

The answer is flexibility.

“Often, clients say, ‘Oh, I don't need a whole meter. My parts don't get to be a meter,’” says Marangell. “But desktop alternatives are typically one to 200 millimeters, with typical customers printing 30 or 40cc parts. Except then they may have the need for one dimension that is longer than the other. What if one dimension is a meter long? Even if the part is not symmetrical, you still have that opportunity to print it out of the BigRep machines in a very efficient footprint.”

The ability to make small, large or high aspect ratio parts on a single machine is a major advantage, as is the possibility of multiple small part builds at the same time.

“It’s like a powerful car,” says Marangell. “When you get on the highway, having that extra capability when you need it is very nice to have, even though when you're driving around the city, you don't use it.”

Big Parts, Big Problems?

Do big parts mean bigger problems for engineers who are used to smaller format builds?

Not necessarily, says Marangell. “Large format machines are a lot more than longer belts and lead screws. Look at the bed. It has to be level down to half the machine resolution, and BigRep systems go down to 0.1mm layer height. So, across a 1-meter square bed, it needs to be level to 0.05mm. That takes some engineering to design a bed that can heat up to 60C to 80C, and in some cases 100C, then cool down without warping or distorting. It's all engineering that makes it reliable.”

The BigRep PRO system uses a unique build methodology that separates the deposition of filament droplets from the melting process, a system that gives finer resolution, especially in corners. The company calls the technology Metering Extruder Technology (MXT), and it employs a Bosch Rexroth CNC Motion Control System to drive the very fine filament feed and motion control needed for high speed, high resolution deposition.

The filament supply is fully enclosed in the machine for tight temperature and humidity control.  The controller monitors these and other machine parameters at sampling rates of up to 500 data points per second, providing a real-time check on machine health. Reliability is especially important in large format printing; it’s not unknown for a build to take a week of run time, and making mistakes is costly due to today’s accelerated development timelines.

Material Selection is Critical

No part or fixture is better than the material from which it’s made. The wrong material choices can mimic the results of poor design or build processes, which means it’s especially important to specify the right material.

There are several key questions: What modulus? What operating conditions? High or low temperatures? Solvents or chemical exposure? Does the part or fixture need high toughness or abrasion resistance?

There are multiple considerations, and for companies looking for very high strength materials, the ability to extrude composites that include polyamide or carbon fiber can give good designers the flexibility to optimize their designs.

Major machine makers such as BigRep have extensive materials libraries and in-house engineering knowledge that can be tapped for a quick start-up and good parts the first time. Large part additive for fixturing or large part making doesn’t have to be any more difficult than prototyping. Start with good advice from your equipment maker, research the material selection and your odds are high for first part success.

To learn more about large format additive manufacturing, visit BigRep America.